1. Field of the Invention
The present invention is a fast acting and environmentally safe, glycol-free liquid which can be applied to a concrete surface to alleviate the slipperiness on public roads, airport runways, railway switches and other objects as well as for eliminating the erosion caused by snow and ice. The composition of the present invention comprises an aqueous solution of urea and ammonium nitrate.
2. Description of the Related Art
One of the fundamental concerns in winter is eliminating the slipperiness associated with snow and ice for pedestrians and vehicles alike. Another concern is the preventing the buildup of snow and ice on railway switches, since a breakdown could result in imminent life-danger.
The bulk of snow and ice is generally removed from a surface by mechanical means (i.e. shovelling, scooping, and sweeping). However, this does not alleviate the slipperiness because an ice film forms and adheres to the surface. On this account, the mechanical means are generally combined with heat transfer, or strewing of chemicals.
The heat transfer can be applied, among others, by a steam sprayer, i.e. by blowing hot steam onto a surface such as an airport runway. This method is costly, hazardous, and the heat-shock damages the concrete. In addition, after the heat transfer is used, an ice film can quickly form when the temperature is under the freezing point in a form often more dangerous than before. Hence, a long-lasting and effective means cannot be obtained by this method.
The most generally used anti-skid chemical is rock salt. Because of its moderate water solubility (above 300 g/liter), it is usually applied to the surface in a solid state. From time to time the rock salt is mixed with sand. The Cl.sup.- ions of the rock salt (and that of the alkaline-earth metal chlorides) act, as pitting corrosion activators, which can heavily damage the iron and steel elements of bridges and overpasses, resulting in decreasing their lifespan which indirectly impedes traffic. The very same goes for damage to gas and water culverts. The rate of the corrosion activated by the Cl.sup.- ions increases if the metallic elements which are embedded in soil are exposed to stray current in the vicinity of D.C. electric transmissions. The peculiarity of the Cl.sup.- ions corrosive effect is especially harmful because of the autocatalytic acceleration of this process caused by continuous accumulation at the corrosion faults, i.e. in the pits. Moreover, the Cl.sup.- ions are stable and no chemical-biological effects can lead to their decomposition, so that they adhere on the metal surface up to its full destruction.
The anions also exert corrosive-erosive effects on concrete as well. The tricalcium-aluminate in the cement forms quaternary hydrates in the presence of water and different anions according to the general formula: 3CaO.Al.sub.2 O.sub.3.3CaX.32H.sub.2 O, where X denotes either a bivalent anion, or two monovalent anions. The molar volume of these quaternary hydrates is much larger than that of the original hydrate so that a very great tensile strength occurs in the course of the crystallization leading to bursting and mouldering of the concrete.
In addition to the corrosion-erosion effects, the sodification of the soil due to the Na.sup.+ ions is also disadvantageous because it damages vegetal life, which indirectly, effect human and animal life. This damage excludes the use of sea-water for irrigation. Therefore, the de-icing with rock salt, is not an effective means.
From a technical viewpoint, a further drawback of applying rock salt is that it does not act quickly and instantaneously which is often required, for example when railway switches' need de-icing. The chemicals in the rock salt, exert a "thawing" effect by decreasing the freezing point of the solution, even under the ambient temperature, when dissolved in water. This leads to the cooling down of the produced liquid wherein the thawing along with the heat transferred from the less cold environment brings about a change in temperature. This mechanism, however, is slower than it would be with use of liquid thawing chemicals (on account of the rate determining role of the liquid formation) since the rock salt dissolution rate is considerably less when there is a decrease in temperature although its solubility (i.e. saturation point) is practically independent thereof. The slow action is not conducive for de-icing switches as well as of other objects whenever the contact time is short. When applying solid rock salt, the uniform portioning out and distribution is much more circumstantial than when liquids' are sprayed out. Although, there are machines that enable uniform distribution of rock salt, these machines can be expensive and the application of the liquid is not available in a large quantity.
According to the state of art it is known that there is a need to reduce the damage due to the corrosion by use of inhibitors, to prevent the modification by chemicals not containing Na.sup.+ ions, and to accelerate the action. However, the agents are applied in the liquid state and these liquids, have many other uses such as in cooling systems of internal combustion. These liquids comprise ethylene-glycol under different trade names and their solutions respectively.
FR 838,638 discloses aqueous solutions of urea in different concentrations that can be combined with rock salt or sodium-hydrocarbonate in order to decrease the freezing point. According to the data given in the patent specification, the urea, by itself, has a freezing point of -10.degree. C., and when in combination with electrolytes has a freezing point of -20.degree. C. This is an obvious advantage of the liquid state when compared to the application of solid urea. The disadvantage to using pure urea is that the action can be slowed down, even in a dissolved state if the temperature is below -8.degree. C. Since urea does not dissociate in aqueous solution, twice the amount is needed to dissolve the identical amount of ice quantity, even compared to the dissociation on rock salt of nearly the same molecular mass. Even if these drawbacks are reduced with the use of electrolytes, the advantage of going without Na.sup.+ ions is lost and, by the same token, the drawback of using Cl.sup.- ions is not avoided either.
U.S. Pat. No. 2,233,185 (1938) describes a frost-resistant liquid wherein the solution comprises formate, acetate, propionate and butyrate salts of alkali metals and their combination respectively in a pH range of 8-9 ensuring it by alkali-borate and phosphate buffer salt additives. Different emulsifying mineral oil derivatives are added as an inhibiter and anti-foaming additives. This solution, on account of the limited availability of the chemicals needed, could not find widespread acceptance in practice even in the course of more than half a century since the patent issued although it exhibits several of the important technical advantages described above.
British Patent No. 561,253 (1994) discloses an aqueous solution of sodium acetate combined with a sodium-chromate inhibitor. The drawback of the Na.sup.+ ions is obviously not eliminated and the method could not be authorized because of the health hazard effect of the chromate ions. Furthermore, the temperature that the solution can work is up to -8.degree. C.
British Patent No. 1,387,810 (1975) discloses a frost resistant de-icing liquid with an aqueous solution of urea and ammonium-chloride and optionally formamide as further component. With this combination, the freezing point of the solution is -16 and -18.degree. C., respectively. Beside the obvious advantage of the solution, there is still the problem, of the Cl.sup.- ions.
U.S. Pat. No. 4,689,165 (1985) discloses a liquid serving for heat transference and isopiestic drying. The liquid is described as an aqueous ammonium-nitrate solution in a wide concentration range and admixed with urea and/or formamide and/or dimethyl-formamide and optionally ethylene-glycol. Thiourea, alkyl-polyglycol-ester, hexamethylene-tetramine and mixtures thereof respectively are used as corrosion inhibitors. This liquid cannot be recommended as de-icing medium for public areas because of the health hazard of some of the components therein. Furthermore, U.S. Pat. No. 4,689,165 does not disclose the ammonium-nitrate--urea quantity ratio and their total concentration that could ensure the advantages of this invention.
It has been a widely known effort for a long time to use by-products from the chemical (e.g. sugar and pharmaceutical) industry for de-icing. However, these efforts are restricted by the rigorous hygienic regulations, by the insufficient reproducibility of the by-products and by their fluctuating supply. Although a CaCl.sub.2 solution is produced by the neutralizing of the waste hydrochloric acid arising from the chlorination in the organic chemical industry with limestone and/or slaked lime and it is of perfect ice thawing effect and the Ca.sup.++ cations are, far from sodificating soil components. The use of CaCl.sub.2 does not eliminate the disadvantages of the Cl.sup.- ions and the uncontrollable origin of the waste hydrochloric acid which runs the risk of environmental pollution.
For de-icing of airport runways and plane surfaces, a number of ethylene-glycol containing liquids have been used which are sprinkled out, usually in an aqueous solution optionally blended with urea and various inhibitors. The toxicity of the glycol and the potential hazard inherent in it contaminating the sweet water and the water used for consumption creates a need for anti-skid measures without glycol.